Thermal transfer element for forming multilayers devices

ABSTRACT

A thermal transfer element for forming a multilayer device may include a substrate and a multicomponent transfer unit that, when transferred to a receptor, is configured and arranged to form a first operational layer and a second operational layer of a multilayer device. In at least some instances, the thermal transfer element also includes a light-to-heat conversion (LTHC) layer that can convert light energy to heat energy to transfer the multicomponent transfer unit. Transferring the multicomponent transfer unit to the receptor may include contacting a receptor with a thermal transfer element having a substrate and a multicomponent transfer unit. Then, the thermal transfer element is selectively heated to transfer the multicomponent transfer unit to the receptor according to a pattern to form at least first and second operational layers of a device. Often, when the thermal transfer element includes a LTHC layer between the substrate and the transfer layer, the thermal transfer element can be illuminated with light according to the pattern and the light energy is converted to heat energy to selectively heat the thermal transfer element.

This application is a divisional of U.S. patent application Ser. No.09/231,723, filed Jan. 15, 1999, U.S. Pat. No. 6,114,088, incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to thermal transfer elements and methods oftransferring layers to form devices on a receptor. In particular, theinvention relates to a thermal transfer element having a multicomponenttransfer unit and methods of using the thermal transfer element forforming a device, such as an optical or electronic device, on areceptor.

BACKGROUND OF THE INVENTION

Many miniature electronic and optical devices are formed using layers ofdifferent materials stacked on each other. These layers are oftenpatterned to produce the devices. Examples of such devices includeoptical displays in which each pixel is formed in a patterned array,optical waveguide structures for telecommunication devices, andmetal-insulator-metal stacks for semiconductor-based devices.

A conventional method for making these devices includes forming one ormore layers on a receptor substrate and patterning the layerssimultaneously or sequentially to form the device. In many cases,multiple deposition and patterning steps are required to prepare theultimate device structure. For example, the preparation of opticaldisplays may require the separate formation of red, green, and bluepixels. Although some layers may be commonly deposited for each of thesetypes of pixels, at least some layers must be separately formed andoften separately patterned. Patterning of the layers is often performedby photolithographic techniques that include, for example, covering alayer with a photoresist, patterning the photoresist using a mask,removing a portion of the photoresist to expose the underlying layeraccording to the pattern, and then etching the exposed layer.

In some applications, it may be difficult or impractical to producedevices using conventional photolithographic patterning. For example,the number of patterning steps may be too large for practicalmanufacture of the device. In addition, wet processing steps inconventional photolithographic patterning may adversely affectintegrity, interfacial characteristics, and/or electrical or opticalproperties of the previously deposited layers. It is conceivable thatmany potentially advantageous device constructions, designs, layouts,and materials are impractical because of the limitations of conventionalphotolithographic patterning. There is a need for new methods of formingthese devices with a reduced number of processing steps, particularlywet processing steps. In at least some instances, this may allow for theconstruction of devices with more reliability and more complexity.

SUMMARY OF THE INVENTION

Generally, the present invention relates to thermal transfer elementsand methods of using thermal transfer elements for forming devices,including optical and electronic devices. One embodiment is a thermaltransfer element that includes a substrate and a multicomponent transferunit that, when transferred to a receptor, is configured and arranged toform at least a first operational layer and a second operational layerof a multilayer device. The first operational layer is configured andarranged to conduct or produce a charge carrier or to produce orwaveguide light. Another embodiment is the device formed using thethermal transfer element. In at least some instances, the thermaltransfer element also includes a light-to-heat conversion (LTHC) layerthat can convert light energy to heat energy to transfer themulticomponent transfer unit. The terms “first operational layer” and“second operational layer” do not imply any order of the layers in thedevice or in the thermal transfer element or the proximity of the twolayers to each other (i.e., there may be one or more layers between thefirst operational layer and the second operational layer.)

Another embodiment is a thermal transfer element that includes asubstrate and a multicomponent transfer unit disposed on the substrate.The multicomponent transfer unit is configured and arranged to form,upon transfer to a receptor, a first operational layer and a secondoperational layer of an electronic component or an optical device. In atleast some instances, this thermal transfer element may also have a LTHClayer.

A further embodiment is a thermal transfer element for forming anorganic electroluminescent (OEL) device. This thermal transfer elementincludes a substrate and a multicomponent transfer unit that isconfigured and arranged to form, upon transfer to a receptor, at leasttwo operational layers of the OEL device, such as, for example, anemitter layer and at least one electrode of the OEL device. Anotherembodiment is an OEL device formed using the thermal transfer element.

Yet another embodiment is a thermal transfer element for forming a fieldeffect transistor. This thermal transfer element includes a substrateand a multicomponent transfer unit that is configured and arranged toform, upon transfer to a receptor, at least two operational layers ofthe field effect transistor, such as a gate insulating layer and asemiconducting layer. Another embodiment is a field effect transistorformed using the thermal transfer element.

Another embodiment is a thermal transfer element for forming awaveguide. This thermal transfer element includes a substrate and amulticomponent transfer unit that is configured and arranged to form,upon transfer to a receptor, at least two operational layers of thewaveguide, such as at least one cladding layer and a core layer. Anotherembodiment is a waveguide formed using the thermal transfer element.

A further embodiment is a method of transferring a multicomponenttransfer unit to a receptor to form a device, including contacting areceptor with a thermal transfer element having a substrate and atransfer layer. The transfer layer includes a multicomponent transferunit. The thermal transfer element is selectively heated to transfer themulticomponent transfer unit to the receptor according to a pattern toform at least a first operational layer and a second operational layerof a device. In at least some instances, the thermal transfer elementincludes a LTHC layer between the substrate and the transfer layer. Thethermal transfer element is illuminated with light according to thepattern and the light energy is converted by the LTHC layer to heatenergy to selectively heat the thermal transfer element.

It will be recognized that thermal transfer elements can also be formedwith a transfer unit that is configured and arranged to transfer asingle layer. It will also be recognized that items, other than devices,may be formed by transferring either a multicomponent transfer unit or asingle layer.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The Figures and the detailed description which follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1A is a schematic cross-section of one example of a thermaltransfer element according to the invention;

FIG. 1B is a schematic cross-section of a second example of a thermaltransfer element according to the invention;

FIG. 1C is a schematic cross-section of a third example of a thermaltransfer element according to the invention;

FIG. 1D is a schematic cross-section of a fourth example of a thermaltransfer element according to the invention;

FIG. 2A is a schematic cross-section of a first example of a transferlayer, according to the invention, for use in any of the thermaltransfer elements of FIGS. 1A to 1D;

FIG. 2B is a schematic cross-section of a second example of a transferlayer, according to the invention, for use in any of the thermaltransfer elements of FIGS. 1A to 1D;

FIG. 2C is a schematic cross-section of a third example of a transferlayer, according to the invention, for use in any of the thermaltransfer elements of FIGS. 1A to 1D;

FIG. 2D is a schematic cross-section of a fourth example of a transferlayer, according to the invention, for use in any of the thermaltransfer elements of FIGS. 1A to 1D;

FIG. 3A is a schematic cross-section of an example of a transfer layer,according to the invention, for use in forming an organicelectroluminescent device;

FIG. 3B is a schematic cross-section of a second example of a transferlayer, according to the invention, for use in forming an organicelectroluminescent device;

FIGS. 4A to 4C are cross-sectional views illustrating steps in oneexample of a process for forming a display device according to theinvention;

FIGS. 5A to 5D are top views illustrating steps in one example of aprocess for forming a field effect transistor according to theinvention;

FIGS. 6A to 6D are cross-sectional views corresponding to FIGS. 5A to5D, respectively, and illustrating steps in the one example of a processfor forming a field effect transistor; and

FIG. 7 is a cross-sectional view of a coupled field effect transistorand organic electroluminescent device, according to the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives, falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is applicable to the formation or partialformation of devices and other objects using thermal transfer andthermal transfer elements for forming the devices or other objects. As aparticular example, a thermal transfer element can be formed for making,at least in part, a multilayer device, such as a multilayer active andpassive device, for example, a multilayer electronic and optical device.This can be accomplished, for example, by thermal transfer of amulticomponent transfer unit of a thermal transfer element. It will berecognized that single layer and other multilayer transfers can also beused to form devices and other objects. While the present invention isnot so limited, an appreciation of various aspects of the invention willbe gained through a discussion of the examples provided below.

The term, “device”, includes an electronic or optical component that canbe used by itself and/or with other components to form a larger system,such as an electronic circuit.

The term, “active device”, includes an electronic or optical componentcapable of a dynamic function, such as amplification, oscillation, orsignal control, and may require a power supply for operation.

The term, “passive device”, includes an electronic or optical componentthat is basically static in operation (i.e., it is ordinarily incapableof amplification or oscillation) and may require no power forcharacteristic operation.

The term, “active layer” includes layers that produce or conduct acharge carrier (e.g., electrons or holes) and/or produce or waveguidelight in a device, such as a multilayer passive or active device.Examples of active layers include layers that act as conducting,semiconducting, superconducting, waveguiding, frequency multiplying,light producing (e.g., luminescing, light emitting, fluorescing orphosphorescing), electron producing, or hole producing layers in thedevice and/or layers that produce an optical or electronic gain in thedevice.

The term, “operational layer” includes layers that are utilized in theoperation of device, such as a multilayer active or passive device.Examples of operational layers include layers that act as insulating,conducting, semiconducting, superconducting, waveguiding, frequencymultiplying, light producing (e.g., luminescing, light emitting,fluorescing or phosphorescing), electron producing, hole producing,magnetic, light absorbing, reflecting, diffracting, phase retarding,scattering, dispersing, refracting, polarizing, or diffusing layers inthe device and/or layers that produce an optical or electronic gain inthe device.

The term, “non-operational layer” includes layers that do not perform afunction in the operation of the device, but are provided solely, forexample, to facilitate transfer of a transfer layer to a receptorsubstrate, to protect layers of the device from damage and/or contactwith outside elements, and/or to adhere the transfer layer to thereceptor substrate.

An active or passive device can be formed, at least in part, by thetransfer of a transfer layer from a thermal transfer element. Thethermal transfer element can be heated by application of directed heaton a selected portion of the thermal transfer element. Heat can begenerated using a heating element (e.g., a resistive heating element),converting radiation (e.g., a beam of light) to heat, and/or applying anelectrical current to a layer of the thermal transfer element togenerate heat. In many instances, thermal transfer using light from, forexample, a lamp or laser, is advantageous because of the accuracy andprecision that can often be achieved. The size and shape of thetransferred pattern (e.g., a line, circle, square, or other shape) canbe controlled by, for example, selecting the size of the light beam, theexposure pattern of the light beam, the duration of directed beamcontact with the thermal transfer element, and the materials of thethermal transfer element.

The thermal transfer element can include a transfer layer that can beused to form, for example, electronic circuitry, resistors, capacitors,diodes, rectifiers, electroluminescent lamps, memory elements, fieldeffect transistors, bipolar transistors, unijunction transistors, MOStransistors, metal-insulator-semiconductor transistors, charge coupleddevices, insulator-metal-insulator stacks, organicconductor-metal-organic conductor stacks, integrated circuits,photodetectors, lasers, lenses, waveguides, gratings, holographicelements, filters (e.g., add-drop filters, gain-flattening filters,cut-off filters, and the like), mirrors, splitters, couplers, combiners,modulators, sensors (e.g., evanescent sensors, phase modulation sensors,interferometric sensors, and the like), optical cavities, piezoelectricdevices, ferroelectric devices, thin film batteries, or combinationsthereof; for example, the combination of field effect transistors andorganic electroluminescent lamps as an active matrix array for anoptical display. Other items may be formed by transferring amulticomponent transfer unit and/or a single layer.

Thermal transfer of layers to form devices is useful, for example, toreduce or eliminate wet processing steps of processes such asphotolithographic patterning which is used to form many electronic andoptical devices. In addition, thermal transfer using light can oftenprovide better accuracy and quality control for very small devices, suchas small optical and electronic devices, including, for example,transistors and other components of integrated circuits, as well ascomponents for use in a display, such as electroluminescent lamps andcontrol circuitry. Moreover, thermal transfer using light may, at leastin some instances, provide for better registration when forming multipledevices over an area that is large compared to the device size. As anexample, components of a display, which has many pixels, can be formedusing this method.

In some instances, multiple thermal transfer elements may be used toform a device or other object. The multiple thermal transfer elementsmay include thermal transfer elements with multicomponent transfer unitsand thermal transfer elements that transfer a single layer. For example,a device or other object may be formed using one or more thermaltransfer elements with multicomponent transfer units and one or morethermal transfer elements that transfer a single layer.

One example of a suitable thermal transfer element 100 is illustrated inFIG. 1A. The thermal transfer element 100 includes a donor substrate102, an optional primer layer 104, a light-to-heat conversion (LTHC)layer 106, an optional interlayer 108, an optional release layer 112,and a transfer layer 110. Directed light from a light-emitting source,such as a laser or lamp, can be used to illuminate the thermal transferelement 100 according to a pattern. The LTHC layer 106 contains aradiation absorber that converts light energy to heat energy. Theconversion of the light energy to heat energy results in the transfer ofa portion of the transfer layer 110 to a receptor (not shown).

Another example of a thermal transfer element 120 includes a donorsubstrate 122, a LTHC layer 124, an interlayer 126, and a transfer layer128, as illustrated in FIG. 1B. Another suitable thermal transferelement 140 includes a donor substrate 142, a LTHC layer 144, and atransfer layer 146, as illustrated in FIG. 1C. Yet another example of athermal transfer element 160 includes a donor substrate 162 and atransfer layer 164, as illustrated in FIG. 1D, with an optionalradiation absorber disposed in the donor substrate 162 and/or transferlayer 164 to convert light energy to heat energy. Alternatively, thethermal transfer element 160 may be used without a radiation absorberfor thermal transfer of the transfer layer 164 using a heating element,such as a resistive heating element, that contacts the thermal transferelement to selectively heat the thermal transfer element and transferthe transfer layer according to a pattern. A thermal transfer element160 without radiation absorber may optionally include a release layer,an interlayer, and/or other layers (e.g., a coating to prevent stickingof the resistive heating element) used in the art.

For thermal transfer using radiation (e.g., light), a variety ofradiation-emitting sources can be used in the present invention. Foranalog techniques (e.g., exposure through a mask), high-powered lightsources (e.g., xenon flash lamps and lasers) are useful. For digitalimaging techniques, infrared, visible, and ultraviolet lasers areparticularly useful. Suitable lasers include, for example, high power(≧100 mW) single mode laser diodes, fiber-coupled laser diodes, anddiode-pumped solid state lasers (e.g., Nd:YAG and Nd:YLF). Laserexposure dwell times can be in the range from, for example, about 0.1 to100 microseconds and laser fluences can be in the range from, forexample, about 0.01 to about 1 J/cm².

When high spot placement accuracy is required (e.g. for high informationfull color display applications) over large substrate areas, a laser isparticularly useful as the radiation source. Laser sources arecompatible with both large rigid substrates such as 1 m×1 m×1.1 mmglass, and continuous or sheeted film substrates, such as 100 μmpolyimide sheets.

Resistive thermal print heads or arrays may be used, for example, withsimplified donor film constructions lacking a LTHC layer and radiationabsorber. This may be particularly useful with smaller substrate sizes(e.g., less than approximately 30 cm in any dimension) or for largerpatterns, such as those required for alphanumeric segmented displays.

Donor Substrate and Optional Primer Layer

The donor substrate can be a polymer film. One suitable type of polymerfilm is a polyester film, for example, polyethylene terephthalate orpolyethylene naphthalate films. However, other films with sufficientoptical properties (if light is used for heating and transfer),including high transmission of light at a particular wavelength, as wellas sufficient mechanical and thermal stability for the particularapplication, can be used. The donor substrate, in at least someinstances, is flat so that uniform coatings can be formed. The donorsubstrate is also typically selected from materials that remain stabledespite heating of the LTHC layer. The typical thickness of the donorsubstrate ranges from 0.025 to 0.15 mm, preferably 0.05 to 0.1 mm,although thicker or thinner donor substrates may be used.

Typically, the materials used to form the donor substrate and the LTHClayer are selected to improve adhesion between the LTHC layer and thedonor substrate. An optional priming layer can be used to increaseuniformity during the coating of subsequent layers and also increase theinterlayer bonding strength between the LTHC layer and the donorsubstrate. One example of a suitable substrate with primer layer isavailable from Teijin Ltd. (Product No. HPE100, Osaka, Japan).

Light-to-Heat Conversion (LTHC) Layer

For radiation-induced thermal transfer a light-to-heat conversion (LTHC)layer is typically incorporated within the thermal transfer element tocouple the energy of light radiated from a light-emitting source intothe thermal transfer element. The LTHC layer preferably includes aradiation absorber that absorbs incident radiation (e.g., laser light)and converts at least a portion of the incident radiation into heat toenable transfer of the transfer layer from the thermal transfer elementto the receptor. In some embodiments, there is no separate LTHC layerand, instead, the radiation absorber is disposed in another layer of thethermal transfer element, such as the donor substrate or the transferlayer. In other embodiments, the thermal transfer element includes anLTHC layer and also includes additional radiation absorber(s) disposedin one or more of the other layers of the thermal transfer element, suchas, for example, the donor substrate or the transfer layer. In yet otherembodiments, the thermal transfer element does not include an LTHC layeror radiation absorber and the transfer layer is transferred using aheating element that contacts the thermal transfer element.

Typically, the radiation absorber in the LTHC layer (or other layers)absorbs light in the infrared, visible, and/or ultraviolet regions ofthe electromagnetic spectrum. The radiation absorber is typically highlyabsorptive of the selected imaging radiation, providing an opticaldensity at the wavelength of the imaging radiation in the range of 0.2to 3, and preferably from 0.5 to 2. Suitable radiation absorbingmaterials can include, for example, dyes (e.g., visible dyes,ultraviolet dyes, infrared dyes, fluorescent dyes, andradiation-polarizing dyes), pigments, metals, metal compounds, metalfilms, and other suitable absorbing materials. Examples of suitableradiation absorbers can include carbon black, metal oxides, and metalsulfides. One example of a suitable LTHC layer can include a pigment,such as carbon black, and a binder, such as an organic polymer. Anothersuitable LTHC layer can include metal or metal/metal oxide formed as athin film, for example, black aluminum (i.e., a partially oxidizedaluminum having a black visual appearance). Metallic and metal compoundfilms may be formed by techniques, such as, for example, sputtering andevaporative deposition. Particulate coatings may be formed using abinder and any suitable dry or wet coating techniques.

Dyes suitable for use as radiation absorbers in a LTHC layer may bepresent in particulate form, dissolved in a binder material, or at leastpartially dispersed in a binder material. When dispersed particulateradiation absorbers are used, the particle size can be, at least in someinstances, about 10 μm or less, and may be about 1 μm or less. Suitabledyes include those dyes that absorb in the IR region of the spectrum.Examples of such dyes may be found in Matsuoka, M., “Infrared AbsorbingMaterials”, Plenum Press, New York, 1990; Matsuoka, M., AbsorptionSpectra of Dyes for Diode Lasers, Bunshin Publishing Co., Tokyo, 1990,U.S. Pat. Nos. 4,722,583; 4,833,124; 4,912,083; 4,942,141; 4,948,776;4,948,778; 4,950,639; 4,940,640; 4,952,552; 5,023,229; 5,024,990;5,156,938; 5,286,604; 5,340,699; 5,351,617; 5,360,694; and 5,401,607;European Patent Nos. 321,923 and 568,993; and Beilo, K. A. et al., J.Chem. Soc., Chem. Commun.,1993, 452-454 (1993), all of which are hereinincorporated by reference. IR absorbers marketed by Glendale ProtectiveTechnologies, Inc., Lakeland, Fla., under the designation CYASORB IR-99,IR-126 and IR-165 may also be used. A specific dye may be chosen basedon factors such as, solubility in, and compatibility with, a specificbinder and/or coating solvent, as well as the wavelength range ofabsorption.

Pigmentary materials may also be used in the LTHC layer as radiationabsorbers. Examples of suitable pigments include carbon black andgraphite, as well as phthalocyanines, nickel dithiolenes, and otherpigments described in U.S. Pat. Nos. 5,166,024 and 5,351,617,incorporated herein by reference. Additionally, black azo pigments basedon copper or chromium complexes of, for example, pyrazolone yellow,dianisidine red, and nickel azo yellow can be useful. Inorganic pigmentscan also be used, including, for example, oxides and sulfides of metalssuch as aluminum, bismuth, tin, indium, zinc, titanium, chromium,molybdenum, tungsten, cobalt, iridium, nickel, palladium, platinum,copper, silver, gold, zirconium, iron, lead, and tellurium. Metalborides, carbides, nitrides, carbonitrides, bronze-structured oxides,and oxides structurally related to the bronze family (e.g., WO_(2.9))may also be used.

Metal radiation absorbers may be used, either in the form of particles,as described for instance in U.S. Pat. No. 4,252,671, incorporatedherein by reference, or as films, as disclosed in U.S. Pat. No.5,256,506, incorporated herein by reference. Suitable metals include,for example, aluminum, bismuth, tin, indium, tellurium and zinc.

As indicated, a particulate radiation absorber may be disposed in abinder. The weight percent of the radiation absorber in the coating,excluding the solvent in the calculation of weight percent, is generallyfrom 1 wt. % to 30 wt. %. preferably from 3 wt. % to 20 wt. %, and mostpreferably from 5 wt. % to 15 wt. %, depending on the particularradiation absorber(s) and binder(s) used in the LTHC.

Suitable binders for use in the LTHC layer include film-formingpolymers, such as, for example, phenolic resins (e.g., novolak andresole resins), polyvinyl butyral resins, polyvinyl acetates, polyvinylacetals, polyvinylidene chlorides, polyacrylates, cellulosic ethers andesters, nitrocelluloses, and polycarbonates. Suitable binders mayinclude monomers, oligomers, or polymers that have been or can bepolymerized or crosslinked. In some embodiments, the binder is primarilyformed using a coating of crosslinkable monomers and/or oligomers withoptional polymer. When a polymer is used in the binder, the binderincludes 1 to 50 wt. %, preferably, 10 to 45 wt. %, polymer (excludingthe solvent when calculating wt. %).

Upon coating on the donor substrate, the monomers, oligomers, andpolymers are crosslinked to form the LTHC. In some instances, ifcrosslinking of the LTHC layer is too low, the LTHC layer may be damagedby the heat and/or permit the transfer of a portion of the LTHC layer tothe receptor with the transfer layer.

The inclusion of a thermoplastic resin (e.g., polymer) may improve, inat least some instances, the performance (e.g., transfer propertiesand/or coatability) of the LTHC layer. It is thought that athermoplastic resin may improve the adhesion of the LTHC layer to thedonor substrate. In one embodiment, the binder includes 25 to 50 wt. %(excluding the solvent when calculating weight percent) thermoplasticresin, and, preferably, 30 to 45 wt. % thermoplastic resin, althoughlower amounts of thermoplastic resin may be used (e.g., 1 to 15 wt. %).The thermoplastic resin is typically chosen to be compatible (i.e., forma one-phase combination) with the other materials of the binder. Asolubility parameter can be used to indicate compatibility, PolymerHandbook, J. Brandrup, ed., pp. VII 519-557 (1989), incorporated hereinby reference. In at least some embodiments, a thermoplastic resin thathas a solubility parameter in the range of 9 to 13 (cal/cm³)^(½),preferably, 9.5 to 12 (cal/cm³)^(½), is chosen for the binder. Examplesof suitable thermoplastic resins include polyacrylics, styrene-acrylicpolymers and resins, and polyvinyl butyral.

Conventional coating aids, such as surfactants and dispersing agents,may be added to facilitate the coating process. The LTHC layer may becoated onto the donor substrate using a variety of coating methods knownin the art. A polymeric or organic LTHC layer is coated, in at leastsome instances, to a thickness of 0.05 μm to 20 μm, preferably, 0.5 μmto 10 μm, and, most preferably, 1 μm to 7 μm. An inorganic LTHC layer iscoated, in at least some instances, to a thickness in the range of 0.001to 10 μm, and preferably, 0.002 to 1 μm.

This LTHC layer can be used in a variety of thermal transfer elements,including thermal transfer elements that have a multicomponent transferunit and thermal transfer elements that are used to transfer a singlelayer of a device or other item. The LTHC layer can be used with thermaltransfer elements that are useful in forming multilayer devices, asdescribed above, as well as thermal transfer elements that are usefulfor forming other items. Examples include such items as color filters,spacer layers, black matrix layers, printed circuit boards, displays(for example, liquid crystal and emissive displays), polarizers, z-axisconductors, and other items that can be formed by thermal transferincluding, for example, those described in U.S. Pat. Nos. 5,156,938;5,171,650; 5,244,770; 5,256,506; 5,387,496; 5,501,938; 5,521,035;5,593,808; 5,605,780; 5,612,165; 5,622,795; 5,685,939; 5,691,114;5,693,446; and 5,710,097 and PCT Patent Applications Nos.98/03346 and97/15173.

Interlayer

An optional interlayer may be used to minimize damage and contaminationof the transferred portion of the transfer layer and may also reducedistortion in the transferred portion of the transfer layer. Theinterlayer may also influence the adhesion of the transfer layer to therest of the thermal transfer element. Typically, the interlayer has highthermal resistance. Preferably, the interlayer does not distort orchemically decompose under the imaging conditions, particularly to anextent that renders the transferred image non-functional. The interlayertypically remains in contact with the LTHC layer during the transferprocess and is not substantially transferred with the transfer layer.

Suitable interlayers include, for example, polymer films, metal layers(e.g., vapor deposited metal layers), inorganic layers (e.g., sol-geldeposited layers and vapor deposited layers of inorganic oxides (e.g.,silica, titania, and other metal oxides)), and organic/inorganiccomposite layers. Organic materials suitable as interlayer materialsinclude both thermoset and thermoplastic materials. Suitable thermosetmaterials include resins that may be crosslinked by heat, radiation, orchemical treatment including, but not limited to, crosslinked orcrosslinkable polyacrylates, polymethacrylates, polyesters, epoxies, andpolyuretharies. The thermoset materials may be coated onto the LTHClayer as, for example, thermoplastic precursors and subsequentlycrosslinked to form a crosslinked interlayer.

Suitable thermoplastic materials include, for example, polyacrylates,polymethacrylates, polystyrenes, polyurethanes, polysulfones,polyesters, and polyimides. These thermoplastic organic materials may beapplied via conventional coating techniques (for example, solventcoating, spray coating, or extrusion coating). Typically, the glasstransition temperature (T_(g)) of thermoplastic materials suitable foruse in the interlayer is 25° C. or greater, preferably 50° C. orgreater, more preferably 100° C. or greater, and, most preferably, 150°C. or greater. The interlayer may be either transmissive, absorbing,reflective, or some combination thereof, at the imaging radiationwavelength.

Inorganic materials suitable as interlayer materials include, forexample, metals, metal oxides, metal sulfides, and inorganic carboncoatings, including those materials that are highly transmissive orreflective at the imaging light wavelength. These materials may beapplied to the light-to-heat-conversion layer via conventionaltechniques (e.g., vacuum sputtering, vacuum evaporation, or plasma jetdeposition).

The interlayer may provide a number of benefits. The interlayer may be abarrier against the transfer of material from the light-to-heatconversion layer. It may also modulate the temperature attained in thetransfer layer so that thermally unstable materials can be transferred.The presence of an interlayer may also result in improved plastic memoryin the transferred material.

The interlayer may contain additives, including, for example,photoinitiators, surfactants, pigments, plasticizers, and coating aids.The thickness of the interlayer may depend on factors such as, forexample, the material of the interlayer, the material of the LTHC layer,the material of the transfer layer, the wavelength of the imagingradiation, and the duration of exposure of the thermal transfer elementto imaging radiation. For polymer interlayers, the thickness of theinterlayer typically is in the range of 0.05 μm to 10 μm, preferably,from about 0.1 μm to 4 μm, more preferably, 0.5 to 3 μm, and, mostpreferably, 0.8 to 2 μm. For inorganic interlayers (e.g., metal or metalcompound interlayers), the thickness of the interlayer typically is inthe range of 0.005 μm to 10 μm, preferably, from about 0.01 μm to 3 μm,and, more preferably, from about 0.02 to 1 μm.

Release Layer

The optional release layer typically facilitates release of the transferlayer from the rest of the thermal transfer element (e.g., theinterlayer and/or the LTHC layer) upon heating of the thermal transferelement, for example, by a light-emitting source or a heating element.In at least some cases, the release layer provides some adhesion of thetransfer layer to the rest of the thermal transfer element prior toexposure to heat. Suitable release layers include, for example,conducting and non-conducting thermoplastic polymers, conducting andnon-conducting filled polymers, and/or conducting and non-conductingdispersions. Examples of suitable polymers include acrylic polymers,polyanilines, polythiophenes, poly(phenylenevinylenes), polyacetylenes,and other conductive organic materials, such as those listed in Handbookof Conductive Molecules and Polymers, Vols. 1-4, H. S. Nalwa, ed., JohnWiley and Sons, Chichester (1997), incorporated herein by reference.Examples of suitable conductive dispersions include inks containingcarbon black, graphite, ultrafine particulate indium tin oxide,ultrafine antimony tin oxide, and commercially available materials fromcompanies such as Nanophase Technologies Corporation (Burr Ridge, Ill.)and Metech (Elverson, Pa.). Other suitable materials for the releaselayer include sublimable insulating materials and sublimablesemiconducting materials (such as phthalocyanines), including, forexample, the materials described in U.S. Pat. No. 5,747,217,incorporated herein by reference.

The release layer may be part of the transfer layer or a separate layer.All or a portion of the release layer may be transferred with thetransfer layer. Alternatively, most or substantially all of the releaselayer remains with the donor substrate when the transfer layer istransferred. In some instances, for example, with a release layerincluding sublimable material, a portion of the release layer may bedissipated during the transfer process.

Transfer Layer

The transfer layer typically includes one or more layers for transfer toa receptor. These one or more layers may be formed using organic,inorganic, organometallic, and other materials. Although the transferlayer is described and illustrated as having discrete layers, it will beappreciated that, at least in some instances, there may be aninterfacial region that includes at least a portion of each layer. Thismay occur, for example, if there is mixing of the layers or diffusion ofmaterial between the layers before, during, or after transfer of thetransfer layer. In other instances, two layers may be completely orpartially mixed before, during, or after transfer of the transfer layer.In any case, these structures will be referred to as including more thanone independent layer, particularly if different functions of the deviceare performed by the different regions.

One example of a transfer layer includes a multicomponent transfer unitthat is used to form a multilayer device, such as an active or passivedevice, on a receptor. In some cases, the transfer layer may include allof the layers needed for the active or passive device. In otherinstances, one or more layers of the active or passive device may beprovided on the receptor, the rest of the layers being included in thetransfer layer. Alternatively, one or more layers of the active orpassive device may be transferred onto the receptor after the transferlayer has been deposited. In some instances, the transfer layer is usedto form only a single layer of the active or passive device or a singleor multiple layer of an item other than a device. One advantage of usinga multicomponent transfer unit, particularly if the layers do not mix,is that the important interfacial characteristics of the layers in themulticomponent transfer unit can be produced when the thermal transferunit is prepared and, preferably, retained during transfer. Individualtransfer of layers may result in less optimal interfaces between layers.

The multilayer device formed using the multicomponent transfer unit ofthe transfer layer may be, for example, an electronic or optical device.Examples of such devices include electronic circuitry, resistors,capacitors, diodes, rectifiers, electroluminescent lamps, memoryelements, field effect transistors, bipolar transistors, unijunctiontransistors, MOS transistors, metal-insulator-semiconductor transistors,charge coupled devices, insulator-metal-insulator stacks, organicconductor-metal-organic conductor stacks, integrated circuits,photodetecltors, lasers, lenses, waveguides, gratings, holographicelements, filters (e.g., add-drop filters, gain-flattening filters,cut-off filters, and the like), mirrors, splitters, couplers, combiners,modulators, sensors (e.g., evanescent sensors, phase modulation sensors,interferometric sensors, and the like), optical cavities, piezoelectricdevices, ferroelectric devices, thin film batteries, or combinationsthereof. Other electrically conductive devices that can be formedinclude, for example, electrodes and conductive elements.

Embodiments of the transfer layer include a multicomponent transfer unitthat is used to form at least a portion of a passive or active device.As an, example, in one embodiment, the transfer layer includes amulticomponent transfer unit that is capable of forming at least twolayers of a multilayer device. These two layers of the multilayer deviceoften correspond to two layers of the transfer layer. In this example,one of the layers that is formed by transfer of the multicomponenttransfer unit is an active layer (i.e., a layer that acts as aconducting, semiconducting, superconducting, waveguiding, frequencymultiplying, light producing (e.g., luminescing, light emitting,fluorescing, or phosphorescing), electron producing, or hole producinglayer in the device and/or as a layer that produces an optical orelectronic gain in the device.) A second layer that is formed bytransfer of the multicomponent transfer unit is another active layer oran operational layer (i.e., a layer that acts as an insulating,conducting, semiconducting, superconducting, waveguiding, frequencymultiplying, light producing (e.g., fluorescing or phosphorescing),electron producing, hole producing, light absorbing, reflecting,diffracting, phase retarding, scattering, dispersing, or diffusing layerin the device and/or as a layer that produces an optical or electronicgain in the device.) The multicomponent transfer unit may also be usedto form additional active layers and/or operational layers, as well as,non-operational layers (i.e., layers that do not perform a function inthe operation of the device, but are provided, for example, tofacilitate transfer of a transfer unit to a receptor substrate and/oradhere the transfer unit to the receptor substrate.)

The transfer layer may include an adhesive layer disposed on an outersurface of the transfer layer to facilitate adhesion to the receptor.The adhesive layer may be an operational layer, for example, if theadhesive layer conducts electricity between the receptor and the otherlayers of the transfer layer, or a non-operational layer, for example,if the adhesive layer only adheres the transfer layer to the receptor.The adhesive layer may be formed using, for example, thermoplasticpolymers, including conducting and non-conducting polymers, conductingand non-conducting filled polymers, and/or conducting and non-conductingdispersions. Examples of suitable polymers include acrylic polymers,polyanilines, polythiophenes, poly(phenylenevinylenes), polyacetylenes,and other conductive organic materials such as those listed in Handbookof Conductive Molecules and Polymers, Vols. 1-4, H. S. Nalwa, ed., JohnWiley and Sons, Chichester (1997), incorporated herein by reference.Examples of suitable conductive dispersions include inks containingcarbon black, graphite, ultrafine particulate indium tin oxide,ultrafine antimony tin oxide, and commercially available materials fromcompanies such as Nanophase Technologies Corporation (Burr Ridge, Ill.)and Metech (Elverson, Pa.).

The transfer layer may also include a release layer disposed on thesurface of the transfer layer that is in contact with the rest of thethermal transfer element. As described above, this release layer maypartially or completely transfer with the remainder of the transferlayer or substantially all of the release layer may remain with thethermal transfer element upon transfer of the transfer layer. Suitablerelease layers are described above.

Although the transfer layer may be formed with discrete layers., it willbe understood that, in at least some embodiments, the transfer layer mayinclude layers that have multiple components and/or multiple uses in thedevice. It will also be understood that, at least in some embodiments,two or more discrete layers may be melted together during transfer orotherwise mixed or combined. In any case, these layers, although mixedor combined, will be referred to as individual layers.

One example of a transfer layer 170, illustrated in FIG. 2A, includes aconductive metal or metal compound layer 172 and a conductive polymerlayer 174 for contact with a receptor (not shown). The conductivepolymer layer 174 may also act, at least in part, as an adhesive layerto facilitate transfer to the receptor. A second example of a transferlayer 180, illustrated in FIG. 2B, includes a release layer 182,followed by a conductive metal or metal compound layer 184, and then aconductive or non-conductive polymer layer 186 for contact with areceptor (not shown). A third example of a transfer layer 190,illustrated in FIG. 2C, includes a conductive inorganic layer 191 (forexample, vapor deposited indium tin oxide), a conductive ornon-conductive polymer layer 192 for contact with a receptor, and anoptional release layer (not shown). A fourth example of a transfer layer195, illustrated in FIG. 2D, consists of a multilayer metal stack 196 ofalternating metals 197, 198, such as gold-aluminum-gold, and aconductive or non-conductive polymer layer 199 for contact with areceptor.

Transfer Layer for an OEL Device

The transfer of a multicomponent transfer unit to form at least aportion of an OEL (organic electroluminescent) device provides anillustrative, non-limiting example of the formation of an active deviceusing a thermal transfer element. In at least some instances, an OELdevice includes a thin layer, or layers, of suitable organic materialssandwiched between a cathode and an anode. Electrons are injected intothe organic layer(s) from the cathode and holes are injected into theorganic layer(s) from the anode. As the injected charges migrate towardsthe oppositely charged electrodes, they may recombine to formelectron-hole pairs which are typically referred to as excitons. Theseexcitons, or excited state species, may emit energy in the form of lightas they decay back to a ground state (see, for example, T. Tsutsui, MRSBulletin, 22, 39-45 (1997), incorporated herein by reference).

Illustrative examples of OEL device constructions include molecularlydispersed polymer devices where charge carrying and/or emitting speciesare dispersed in a polymer matrix (see J. Kido “OrganicElectroluminescent devices Based on Polymeric Materials”, Trends inPolymer Science, 2, 350-355 (1994), incorporated herein by reference),conjugated polymer devices where layers of polymers such aspolyphenylene vinylene act as the charge carrying and emitting species(see J. J. M. Halls et al., Thin Solid Films, 276, 13-20 (1996), hereinincorporated by reference), vapor deposited small moleculeheterostructure devices (see U.S. Pat. No. 5,061,569 and C. H. Chen etal., “Recent Developments in Molecular Organic ElectroluminescentMaterials”, Macromolecular Symposia, 125, 1-48 (1997), hereinincorporated by reference), light emitting electrochemical cells (see Q.Pei et al., J. Amer. Chem. Soc., 118, 3922-3929 (1996), hereinincorporated by reference), and vertically stacked organiclight-emitting diodes capable of emitting light of multiple wavelengths(see U.S. Pat. No. 5,707,745 and Z. Shen et al., Science, 276, 2009-2011(1997), herein incorporated by reference).

One suitable example of a transfer layer 200 for forming an OEL deviceis illustrated in FIG. 3A. The transfer layer 200 includes an anode 202,a hole transport layer 204, an electron transport/emitter layer 206, anda cathode, 208. Alternatively, either the cathode or anode can beprovided separately on a receptor (e.g., as a conductive coating on thereceptor) and not in the transfer layer. This is illustrated in FIG. 3B,for an anode-less transfer layer 200′ using primed reference numerals toindicate layers in common with the transfer layer 200.

The transfer layer 200 may also include one or more layers, such as arelease layer 210 and/or an adhesive layer 212, to facilitate thetransfer of the transfer layer to the receptor. Either of these twolayers can be conductive polymers to facilitate electrical contact witha conductive layer or structure on the receptor or conductive layer(s)formed subsequently on the transfer layer. It will be understood thatthe positions of the release layer and adhesive layer could be switchedwith respect to the other layers of the transfer layer.

The anode 202 and cathode 208 are typically formed using conductingmaterials such as metals, alloys, metallic compounds, metal oxides,conductive ceramics, conductive dispersions, and conductive polymers,including, for example, gold, platinum, palladium, aluminum, titanium,titanium nitride, indium tin oxide (ITO), fluorine tin oxide (FTO), andpolyaniline. The anode 202 and the cathode 208 can be single layers ofconducting materials or they can include multiple layers. For example,an anode or a cathode may include a layer of aluminum and a layer ofgold or a layer of aluminum and a layer of lithium fluoride. For manyapplications, such as display applications, it is preferred that atleast one of the cathode and anode be transparent to the light emittedby the electroluminescent device.

The hole transport layer 204 facilitates the injection of holes into thedevice and their migration towards the cathode 208. The hole transportlayer 204 further acts as a barrier for the passage of electrons to theanode 202. The hole transport layer 204 can include, for example, adiamine derivative, such asN,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (also known as TPD).

The electron transport/emitter layer 206 facilitates the injection ofelectrons and their migration towards the anode 202. The electrontransport/emitter layer 206 further acts as a barrier for the passage ofholes to the cathode 208. The electron transport/emitter layer 206 isoften formed from a metal chelate compound, such as, for example,tris(8-hydroxyquinoline) aluminum (ALQ).

The interface between the hole transport layer 204 and electrontransport/emitter layer 206 forms a barrier for the passage of holes andelectrons and thereby creates a hole/electron recombination zone andprovides an efficient organic electroluminescent device. When theemitter material is ALQ, the OEL, device emits blue-green light. Theemission of light of different colors may be achieved by the use ofdifferent emitters and dopants in the electron transport/emitter layer206 (see C. H. Chen et al., “Recent Developments in Molecular OrganicElectroluminescent Materials”, Macromolecular Symposia, 125, 1-48(1997), herein incorporated by reference).

Other OEL multilayer device constructions may be transferred usingdifferent transfer layers. For example, the hole transporting layer 204in FIG. 3A could also be an emitter layer and/or the hole transportinglayer 204 and the electron transporting/emitter layer 206 could becombined into one layer. Furthermore, a separate emitter layer could beinterposed between layers 204 and 206 in FIG. 3A.

The multilayer unit can be transferred onto a receptor to form OELdevices. As an example, an optical display can be formed as illustratedin FIGS. 4A through 4C. For example, green OEL devices 302 can betransferred onto the receptor substrate 300, as shown in FIG. 4A.Subsequently, blue OEL devices 304 and then red OEL devices 306 may betransferred, as shown in FIGS. 4B and 4C. Each of the green, blue, andred OEL devices 302, 304, 306 are transferred separately using green,blue, and red thermal transfer elements, respectively. Alternatively,the red, green, and blue thermal transfer elements could be transferredon top of one another to create a multi-color stacked OLED device of thetype disclosed in U.S. Pat. No. 5,707,745, herein incorporated byreference. Another method for forming a full color device includesdepositing columns of hole transport layer material and thensequentially depositing red, green, and blue electron transportlayer/emitter multicomponent transfer units either parallel orperpendicular to the hole transport material. Yet another method forforming a full color device includes depositing red, green, and bluecolor filters (either conventional transmissive filters, fluorescentfilters, or phosphors) and then depositing multicomponent transfer unitscorresponding to white light or blue light emitters.

After formation, the OEL device is typically coupled to a driver (notshown) and sealed to prevent damage. The thermal transfer element can bea small or a relatively large sheet coated with the appropriate transferlayer. The use of laser light or other similar light-emitting sourcesfor transferring these devices permits the formation of narrow lines andother shapes from the thermal transfer element. A laser or other lightsource could be used to produce a pattern of the transfer layer on thereceptor, including receptors that may be meters in length and width.

This example illustrates advantages of using the thermal transferelements. For example, the number of processing steps can be reduced ascompared to conventional photolithography methods because many of thelayers of each OEL device are transferred simultaneously, rather thanusing multiple etching and masking steps. In addition, multiple devicesand patterns can be created using the same imaging hardware. Only thethermal transfer element needs to be changed for each of the differentdevices 302, 304, 306.

Transfer Layer for a Field Effect Transistor

A field effect transistor (FET) can be formed using one or more thermaltransfer elements. One example of an organic field effect transistorthat could be formed using thermal transfer elements is described inGarnier, et al., Adv. Mater. 2, 592-594 (1990), incorporated herein byreference.

Field effect transistors are, in general, three terminal electronicdevices capable of modulating the current flow between two terminals(source and drain) with the application of an electric field at theremaining terminal (gate) (see, for example, S. M. Sze, Physics ofSemiconductor Devices, 2^(nd) Ed. Wiley, New York, 431-435 (1981),incorporated herein by reference). In one representative construction, afield effect transistor consists of a rectangular slab of semiconductingmaterial bounded on opposite ends with two electrodes—the source anddrain electrodes. On one of the other surfaces an insulating layer (gatedielectric) and subsequent electrode (gate electrode) are formed. Anelectric field is applied between the gate electrode and thesemiconductor slab. The conductivity, and therefore current flow,between the source and drain electrodes is controlled by the polarityand strength of the gate-insulator-semiconductor field.

It is also possible to construct a field effect transistor without agate insulator. Field effect transistors can be assembled with a gateelectrode/semiconductor rectifying region. The conductivity between thesource and drain electrodes is modulated by varying the polarity andstrength of the gate/semiconductor field which controls the depletionregion at the gate/semiconductor interface. This type of construction istypically referred to as a MESFET or JFET, metal semiconductor FET orJunction FET respectively (see, for example, S. M. Sze, Physics ofSemiconductor Devices, 2^(nd) Ed. Wiley, New York, 312-324 (1981),incorporated herein by reference).

Material selection for the metal electrodes, gate dielectric andsemiconductor may be influenced several parameters includingconductivity, reliability, electron affinity, fermi level, processingcompatibility, device application, and cost. For example, in general, itis advantageous to select a metal with a low work function to form anelectrical contact with an n-type (electron conducting) semiconductor.

An example of the formation of a field effect transistor is illustratedin FIGS. 4A to 4D and 5A to 5D. The field effect transistor is formed ona receptor substrate 500 upon which electrical contacts 502, 504, 506,508 have been formed, as illustrated in FIGS. 4A and 5A. The receptorsubstrate 500 is typically formed from a non-conducting material, suchas glass or a non-conducting plastic or the receptor substrate 500 iscovered with a non-conductive coating. The electrical contacts 502, 504,506, 508 can be formed using a metal or a metallic compound, such asgold, silver, copper, or indium tin oxide. The electrical contacts 502,504, 506, 508 can also be formed using a conducting organic materialsuch as polyaniline. The electrical contacts 502, 504, 506, 508 can beformed by a variety of techniques including photolithography or thermaltransfer utilizing a thermal transfer element with a transfer layer ofthe particular metal, metallic compound, or conducting organic material.

A gate electrode 510 is formed between two opposing electrodes 502, 506,as illustrated in FIGS. 4B and 5B. The gate electrode 510 can be formedusing a first thermal transfer element with a transfer layer includingthe material chosen for the gate electrode. Suitable materials for thegate electrode include metals, metallic compounds, conducting polymers,filled polymers, and conducting inks. Examples of materials for the gateelectrode include gold, silver, platinum, carbon, indium tin oxide,polyaniline, and carbon black filled polymers.

A gate insulating layer 512 and a semiconductor layer 514 are formedover the gate electrode 510, as shown in FIGS. 4C and 5C. These twolayers 512, 514 can be formed using a second thermal transfer elementthat includes, for example, a multicomponent transfer unit with aninsulating layer and a semiconductor layer. The gate insulating layer512 can be formed using organic or inorganic insulators, such as silicondioxide, silicon nitride, tantalum oxide, other inorganic oxides,polyimides, polyamic acids, acrylics, cyanoethylpullulan, and magnesiumfluoride. The organic polymers used as gate insulating layers may befilled with, an insulating material such as ultrafine silica particles.

The semiconductor layer 514 can be formed using organic and inorganicsemiconductors, such as polythiophenes, oligomeric thiophenes,polyphenylvinylenes, polyacetylenes, metallophthalocyanines, andamorphous and polycrystalline silicon and germanium.

Finally, source and drain contacts 516, 518 can be formed usingconductive material, such as a metal, metallic compound, conductingpolymer, conducting ink, or conducting organic material as describedabove to make two spaced apart connections between the semiconductinglayer 514 and opposing electrical contacts 504, 508, respectively, asshown in FIGS. 4D and 5D. The region 520 between the source and draincontacts 516, 518 forms a channel of the field effect transistor. Thesource and drain contacts 516, 518 can be formed using a third thermaltransfer layer including a transfer layer with a layer of theappropriate conductive material. It will be recognized that in manyfield effect transistors, the identity of the source and drain can beinterchanged from the device illustrated in FIGS. 4D and 5D.

An OEL device 600 and field effect transistor 610 can be combined, forexample, where one of the electrical contacts of the transistor is alsothe anode or cathode 620 of the OEL device, as shown in FIG. 7. Thiscombination allows the field effect transistor to control the operationof the OEL device. A display unit with this combination can be madeusing, for example, three or more thermal transfer elements to form thefield effect transistor and at least one additional thermal transferelement to form the OEL device, as described above.

Transfer Layer for an Optical Waveguide

Optical waveguides typically include a core of material that issubstantially transparent to light of the wavelength of interest. Thecore is covered by a cladding material that is also is substantiallytransparent to the light of the wavelength of interest. The light istransmitted through, and substantially confined in, the core of thewaveguide by total internal reflectance caused by the difference in theindex of refraction between the core and the cladding. Typically, theindex of refraction of the core is slightly greater than the index ofrefraction of the cladding. The performance of a waveguide is influencedby many factors such as, for example, the shape, length, andtransparency of the waveguide and the difference in refractive indexbetween the core and the cladding. Typically, a difference in refractiveindex between the core and the cladding of 0.002 to 0.5 is desirable.These variables can be manipulated by those skilled in the art tofabricate waveguides with performance optimized for their intended use.Core and cladding materials that are useful in forming waveguidesinclude glass and organic polymers.

Conventionally, optical waveguides are manufactured by a variety ofmethods, such as photolithography, diffusion, and ion implantationprocesses. For example, a conventional waveguide can be manufactured byapplying a suitable optical material onto a substrate, typically in asandwich form, resulting in a core region surrounded by a claddingregion. A photoresist material is then applied onto the sandwich andpatterned by a photolithographic process. The pattern defined by thephotolithographic process is then transferred to the waveguide sandwichby an etching process. The substrate with the etched pattern is thencleaned, which removes the remaining photoresist and leaves theresultant waveguide on the substrate.

An optical waveguide can be formed using one or more thermal transferelements. For example, thermal transfer using thermal transfer element100 in FIG. 1A wherein transfer layer 110 comprises three layers ofpolymers of suitable indices of refraction could be used to form awaveguide on a receptor substrate. Since it forms the core of thewaveguide, the central polymer layer of the transfer layer typically hasan index of refraction slightly greater than the outer two layers.Examples of core/cladding combinations include, but are not limited to.polyetherimide/benzocyclobutene, polycarbonate/fluorinated acrylic,polycarbonate/polymethylmethacrylate and fluorinatedpolyimide/polymethylmethacrylate.

Thermal transfer of portions of an optical waveguide using a thermaltransfer element may also be utilized to form an optical waveguide. Forexample, a receptor substrate could be coated with a cladding polymersuch as polymethylmethacrylate by conventional methods or by a separatethermal transfer element and thermal transfer step. Subsequent thermaltransfer of a polymethylmethacrylate/polycarbonate bilayer to thereceptor substrate forms a waveguide having a polycarbonate core andpolymethylmethacrylate cladding.

Receptor

The receptor substrate may be any item suitable for a particularapplication including, but not limited to, transparent films, displayblack matrices, passive and active portions of electronic displays,metals, semiconductors, glass, various papers, and plastics.Non-limiting examples of receptor substrates which can be used in thepresent invention include anodized aluminum and other metals, plasticfilms (e.g., polyethylene terephthalate, polypropylene), indium tinoxide coated plastic films, glass, indium tin oxide coated glass,flexible circuitry, circuit boards, silicon or other semiconductors, anda variety of different types of paper (e.g., filled or unfilled,calendered, or coated). Various layers (e.g., an adhesive layer) may becoated onto the receptor substrate to facilitate transfer of thetransfer layer to the receptor substrate. Other layers may be coated onthe receptor substrate to form a portion of a multilayer device. Forexample, an OEL or other electronic device may be formed using areceptor substrate having a metal anode or cathode formed on thereceptor substrate prior to transfer of the transfer layer from thethermal transfer element. This metal anode or cathode may be formed, forexample, by deposition of a conductive layer on the receptor substrateand patterning of the layer into one or more anodes or cathodes using,for example, photolithographic techniques.

Operation

During imaging, the thermal transfer element is typically brought intointimate contact with a receptor. In at least some instances, pressureor vacuum are used to hold the thermal transfer element in intimatecontact with the receptor. A radiation source is then used to heat theLTHC layer (and/or other layer(s) containing radiation absorber) in animagewise fashion (e.g., digitally or by analog exposure through a mask)to perform imagewise transfer of the transfer layer from the thermaltransfer element to the receptor according to a pattern.

Alternatively, a heating element, such as a resistive heating element,may be used to transfer the multicomponent transfer unit. The thermaltransfer element is selectively contacted with the heating element tocause thermal transfer of a portion of the transfer layer according to apattern. In another embodiment, the thermal transfer element may includea layer that can convert an electrical current applied to the layer intoheat.

Typically, the transfer layer is transferred to the receptor withouttransferring any of the other layers of the thermal transfer element,such as the optional interlayer and the LTHC layer. The presence of theoptional interlayer may eliminate or reduce the transfer of the LTHClayer to the receptor and/or reduce distortion in the transferredportion of the transfer layer. Preferably, under imaging conditions, theadhesion of the interlayer to the LTHC layer is greater than theadhesion of the interlayer to the transfer layer. In some instances, areflective interlayer can be used to attenuate the level of imagingradiation transmitted through the interlayer and reduce any damage tothe transferred portion of the transfer layer that may result frominteraction of the transmitted radiation with the transfer layer and/orthe receptor. This is particularly beneficial in reducing thermal damagewhich may occur when the receptor is highly absorptive of the imagingradiation.

During laser exposure, it may be desirable to minimize formation ofinterference patterns due to multiple reflections from the imagedmaterial. This can be accomplished by various methods. The most commonmethod is to effectively roughen the surface of the thermal transferelement on the scale of the incident radiation as described in U.S. Pat.No. 5,089,372. This has the effect of disrupting the spatial coherenceof the incident radiation, thus minimizing self interference. Analternate method is to employ an antireflection coating within thethermal transfer element. The use of anti-reflection coatings is known,and may consist of quarter-wave thicknesses of a coating such asmagnesium fluoride, as described in U.S. Pat. No. 5,171,650,incorporated herein by reference.

Large thermal transfer elements can be used, including thermal transferelements that have length and width dimensions of a meter or more. Inoperation, a laser can be rastered or otherwise moved across the largethermal transfer element, the laser being selectively operated toilluminate portions of the thermal transfer element according to adesired pattern. Alternatively, the laser may be stationary and thethermal transfer element moved beneath the laser.

In some instances, it may be necessary, desirable, and/or convenient tosequentially use two or more different thermal transfer elements to forma device. For example, one thermal transfer element may be used to forma gate electrode of a field effect transistor and another thermaltransfer element may be used to form the gate insulating layer andsemiconducting layer, and yet another thermal transfer layer may be usedto form the source and drain contacts. A variety of other combinationsof two or more thermal transfer elements can be used to form a device,each thermal transfer element forming one or more layers of the device.Each of these thermal transfer elements may include a multicomponenttransfer unit or may only include a single layer for transfer to thereceptor. The two or more thermal transfer units are then sequentiallyused to deposit one or more layers of the device. In some instances, atleast one of the two or more thermal transfer elements includes amulticomponent transfer unit.

EXAMPLES

Unless otherwise indicated, chemicals were obtained from AldrichChemical Company (Milwaukee, Wis.). All of the vacuum depositedmaterials were thermally evaporated and deposited at room temperature.The deposition rate and thickness of each vacuum deposited layer wasmonitored with a quartz crystal microbalance (Leybold Inficon Inc., EastSyracuse, N.Y.). The background pressure (chamber pressure prior to thedeposition) was roughly 1×10⁻⁵ torr (1.3×10⁻³ Pa).

The laser transfer system included a CW Nd:YAG laser, acousto-opticmodulator, collimating and beam expanding optics, an optical isolator, alinear galvonometer and an f-theta scan lens. The Nd:YAG laser wasoperating in the TEM 00 mode, and produced a total power of 7.5 Watts.Scanning was accomplished with a high precision linear galvanometer(Cambridge Technology Inc., Cambridge, Mass.). The laser was focused toa Gaussian spot with a measured diameter of 140 μm at the 1/e² intensitylevel. The spot was held constant across the scan width by utilizing anf-theta scan lens. The laser spot was scanned across the image surfaceat a velocity of 5.6 meters/second. The f-theta scan lens held the scanvelocity uniform to within 0.1%, and the spot size constant to within ±3microns.

Example 1 Preparation of a Substrate/LTHC/Interlayer Element

A carbon black light-to-heat conversion layer was prepared by coatingthe following LTHC Coating Solution, according to Table 1, onto a 0.1 mmPET substrate with a Yasui Seiki Lab Coater, Model CAG-150 (Yasui SeikiCo., Bloomington, Ind.) using a microgravure roll of 381 helical cellsper lineal cm (150 helical cells per lineal inch).

TABLE 1 LTHC Coating Solution Parts by Component Weight Raven ™ 760Ultra carbon black pigment (available 3.39 from Columbian Chemicals,Atlanta, GA) Butvar ™ B-98 (polyvinylbutyral resin, available from 0.61Monsanto, St. Louis, MO) Joncryl ™ 67 (acrylic resin, available fromS.C. 1.81 Johnson & Son, Racine, WI) Elvacite ™ 2669 (acrylic resin,available from ICI 9.42 Acrylics, Wilmington, DE) Disperbyk ™ 161(dispersing aid, available from Byk 0.3 Chemie, Wallingford, CT)FC-430 ™ (fluorochemical surfactant, available from 0.012 3M, St. Paul,MN) Ebecryl ™ 629 (epoxy novolac acrylate, available from 14.13 UCBRadcure, N. Augusta, SC) Irgacure ™ 369 (photocuring agent, availablefrom Ciba 0.95 Specialty Chemicals, Tarrytown, NY) Irgacure ™ 184(photocuring agent, available from Ciba 0.14 Specialty Chemicals,Tarrytown, NY) propylene glycol methyl ether acetate 16.78 1-methoxy-2-propanol 9.8 methyl ethyl ketone 42.66

The coating was in-line dried at 40° C. and UV-cured at 6.1 m/min usinga Fusion Systems Model 1600 (400 W/in) UV curing system fitted withH-bulbs (Fusion UV Systems, Inc., Gaithersburg, Md.). The dried coatinghad a thickness of approximately 3 microns.

Onto the carbon black coating of the light-to-heat conversion layer wasrotogravure coated an Interlayer Coating Solution, according to Table 2,using the Yasui Seiki Lab Coater, Model CAG-150 (Yasui Seiki Co.,Bloomington, Ind.). This coating was in-line dried (40° C.) and UV-curedat 6.1 m/min using a Fusion Systems Model 1600 (600 W/in) fitted withH-bulbs. The thickness of the resulting interlayer coating wasapproximately 1.7 microns.

TABLE 2 Interlayer Coating Solution Parts by Component Weight Butvar ™B-98 0.98 Joncryl ™ 67 2.95 Sartomer ™ SR351 ™ (trimethylolpropane 15.75triacrylate, available from Sartomer, Exton, PA) Irgacure ™ 369 1.38Irgacure ™ 184 0.2 1-methoxy-2-propanol 31.5 methyl ethyl ketone 47.24

Example 2 Preparation of another Substrate/LTHC/Interlayer Element

A carbon black light-to-heat conversion layer was prepared by coatingthe following LTHC Coating Solution, according to Table 3, onto a 0.1 mmPET substrate with a Yasui Seiki Lab Coater, Model CAG-150 (Yasui SeikiCo., Bloomington, Ind.) using a microgravure roll of 228.6 helical cellsper lineal cm (90 helical cells per lineal inch).

TABLE 3 LTHC Coating Solution Parts by Component Weight Raven ™ 760Ultra carbon black pigment (available 3.78 from Columbian Chemicals,Atlanta, GA) Butvar ™ B-98 (polyvinylbutyral resin, available 0.67 fromMonsanto, St. Louis, MO) Joncryl ™ 67 (acrylic resin, available fromS.C. 2.02 Johnson & Son, Racine, WI) Disperbyk ™ 161 (dispersing aid,available from Byk 0.34 Chemie, Wallingford, CT) FC-430 ™(fluorochemical surfactant, available from 0.01 3M, St. Paul, MN) SR351 ™ (trimethylolpropane triacrylate, available 22.74 from Sartomer,Exton, PA) Duracure ™ 1173 (2-hydroxy-2-methyl-1-phenyl-1- 1.48propanone photoinitiator, available from Ciba, Hawthorne, NY)1-methoxy-2-propanol 27.59 methyl ethyl ketone 41.38

The coating was in-line dried at 40° C. and UV-cured at 6.1 n/min usinga Fusion Systems Model 1600 (400 W/in) UV curing system fitted withH-bulbs. The dried coating had a thickness of approximately 3 microns.

Onto the carbon black coating of the light-to-heat conversion layer wasrotogravure coated an Interlayer Coating Solution, according to Table 4,using the Yasui Seiki Lab Coater, Model CAG-150 (Yasui Seiki Co.,Bloomington, Ind.). This coating was in-line dried (40° C.) and UV-curedat 6.1 m/min using a Fusion Systems Model 1600 (600 W/in) fitted withH-bulbs. The thickness of the resulting interlayer coating wasapproximately 1.7 microns.

TABLE 4 Interlayer Coating Solution Parts by Component Weight Butvar ™B-98 0.99 Joncryl ™ 67 2.97 SR 351 ™ 15.84 Duracure ™ 1173 0.991-methoxy-2-propanol 31.68 methyl ethyl ketone 47.52

Example 3 Transfer of a Polymer/Gold/Polymer Film

A thermal donor element with a multicomponent transfer layer wasprepared by applying coatings to the substrate/LTHC/interlayer elementof Example 2. A coating of acrylic polymer (Elvacite™ 2776, ICIAcrylics, Wilmington, Del.) was applied to the interlayer of the thermaltransfer element using a 5 wt. % aqueous solution of polymer with a #6Mayer bar. The coating was dried at about 60° C. for about 5 minutes. A500 Å coating of gold was then vacuum deposited over the acrylicpolymer. Another coating of acrylic polymer (Elvacite™ 2776, ICIAcrylics) was coated over the gold layer by applying a 5 wt. % aqueoussolution of polymer with a #6 Mayer bar. The coating was dried at about60° C. for about 5 minutes. The sample was imaged onto a glass receptorusing a linear scan speed of 5.6 m/s. The result was a uniform transferof the polymer/gold/polymer transfer layer as 70 micron wide lines withexcellent edge uniformity.

Example 4 Transfer of Polymer/Tin/Gold/Tin/Polymer Film

A thermal donor element with a multicomponent transfer layer wasprepared by applying coatings to the substrate/LTHC/interlayer elementof Example 2. A coating of acrylic polymer (Elvacite™ 2776, ICIAcrylics) was applied to the interlayer of the thermal transfer elementusing a 5 wt. % aqueous solution of polymer with a #6 Mayer bar. Thecoating was dried at about 60° C. for about 5 minutes. A 500 Å coatingof tin was vacuum deposited on top of the acrylic polymer. A 500 Åcoating of gold was then vacuum deposited on the tin. Then, a second 500A coating of tin was vacuum deposited on the gold. A second coating ofacrylic polymer (Elvacite™ 2776, ICd Acrylics) was prepared by applyinga 5 wt. % aqueous solution of polymer with a #6 Mayer bar. The coatingwas dried at about 60° C. for about 5 minutes. The thermal transferelement was imaged onto a glass receptor using a linear scan speed of5.6 m/s. The result was a uniform transfer of apolymer/tin/gold/tin/polymer film as 70 micron wide lines with excellentedge uniformity.

Example 5 Hole Transport Thermal Transfer Element

A hole transport thermal transfer element was formed using thesubstrate/LTHC/interlayer element of Example 1. A hole transport coatingsolution, formed by mixing the components of Table 5, was coated ontothe interlayer using a #6 Mayer bar. The coating was dried for 10 min at60° C.

TABLE 5 Hole Transport Coating Solution Weight Component (g)N,N′-bis(3-methylphenyl)-N,N′- 2.5 diphenylbenzidine polyvinylcarbazole2.5 cyclohexanone 97.5 propylene glycol methyl ether acetate 97.5(PGMEA)

Example 6 OEL Thermal Transfer Element

An OEL thermal transfer element with a multicomponent transfer layer wasprepared by applying coatings to a substrate/LTHC/interlayer elementformed according to Example 1. A 200 Å layer of copper phthalocyaninewas deposited on the interlayer as a semiconducting release layer. Next,a 250 Å layer of aluminum was deposited as a cathode layer. A 10 Å layerof lithium fluoride was deposited on the aluminum. Next, a 300 Å layerof tris(8-hydroxyquinolinato) aluminum (ALQ) was deposited as anelectron transport layer. Finally, a 200 A layer ofN,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) was deposited as ahole transport layer.

Example 7 Preparation of an OEL Device

A receptor substrate of glass covered with indium tin oxide (ITO) (10Ω/square, Thin Film Devices Inc., Anaheim, Calif.) was used to form theanode of the OEL device. First, the Hole Transport thermal transferelement of Example 5 was imaged onto the receptor. This was followed byimaging of the OEL thermal transfer element of Example 6 to complete theOEL device.

In each transfer, the transfer layer side of the thermal transferelement was held in intimate contact with the receptor in a vacuumchuck. A laser was directed to be incident upon the substrate side ofthe thermal transfer elements. The exposures were performed so that thetwo transfer layers were transferred with correct registration. Thisproduced 120 μm wide lines. The final OEL device had layers in thefollowing order (from top to bottom):

Aluminum Cathode

Lithium Fluoride

ALQ Electron Transport Layer/Emitter

TPD Hole Transport Layer (from OEL thermal transfer element)

TPD Hole Transport Layer (from Hole Transport thermal transfer element)

Glass Receptor

Electrical contact was made at the ITO anode and the aluminum cathode.When a potential was applied, the OEL device produced visuallydetectable light. The injection current was monitored as a function ofthe applied potential (voltage) which was continuously swept from 0volts to 10-30 volts. At one point 70 PA at 10 volts flowing through a42 mm×80 μm device was measured. This corresponds to a current densityof about 2 mA/cm². The current density is well within the normaloperating range of small molecule devices fabricated directly onto areceptor to substrate using conventional techniques.

Example 8 Another OEL Thermal Transfer Element

An OEL thermal transfer element with a multicomponent transfer layer wasprepared by applying coatings to a substrate/LTHC/interlayer elementprepared according to Example 1. A primer solution A, according to Table6, was first coated using a #3 Mayer bar. The coating was dried at about60° C. for about 5 minutes.

TABLE 6 Primer Solution Component Source Weight (g) PVP K-90 (polyvinylInternational Specialty 2 pyrrolidone) Products (Wayne, NJ) PVA GohsenolKL-03 Nippon Gohsei (Osaka, 2 (polyvinyl alcohol) Japan) Elvacite 2776(acrylic polymer) ICI Acrylics 4 DMEA (dimethylethanolamine) Aldrich 0.82-butoxyethanol Aldrich 0.8 deionized water — 150.4

A 200 Å layer of copper phthalocyanine was deposited as a semiconductingrelease layer on the primer layer. Next, a 250 Å layer of aluminum wasdeposited as a cathode layer. A 10 Å layer of lithium fluoride wasdeposited on the aluminum. Next, a 300 Å layer oftris(8-hydroxyquinolinato) aluminum (ALQ) was deposited as an electrontransport layer. Finally, a 200 Å layer ofN,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) was deposited as ahole transport layer.

Example 9 Transfer of a Partial OEL Transfer Layer to a FlexibleSubstrate

The receptor substrate consisted of a piece of 4 mil (about 100 μm)polyethyleneterephthalate (PET) film (unprimed HPE100,Teijin Ltd.,Osaka, Japan). First, the Hole Transport thermal transfer element ofExample 5 was imaged onto the receptor. Then the OEL thermal transferelement of Example 8 was imaged onto the hole transport layer.

In each transfer, the transfer layer side of the thermal transferelement was held in intimate contact with the receptor in a vacuumchuck. A laser was directed to be incident upon the substrate side ofthe thermal transfer elements. The exposures were performed so that thetwo layers with correct registration. This produced 120 μm wide lines.The final construction had layers in the following order (from top tobottom):

Aluminum Cathode

Lithium Fluoride

ALQ Electron Transport Layer/Emitter

TPD Hole Transport Layer (from OEL Thermal Transfer Element)

TPD Hole Transport Layer (from Hole Transport thermal transfer element)

PET Receptor

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

We claim:
 1. A thermal transfer element comprising: a substrate; and amulticomponent transfer unit that, when transferred to a receptor, isconfigured and arranged to form a first operational layer and a secondoperational layer of a multilayer device, wherein the first operationallayer is configured and arranged to produce or waveguide light, andwherein the second operational layer is capable of conducting orsemiconducting a charge carrier, producing a charge carrier, producinglight, or waveguiding light.
 2. The thermal transfer element of claim 1,wherein the multicomponent transfer unit is configured and arranged toform at least one additional layer of the multilayer device.
 3. Thethermal transfer element of claim 1, wherein the multicomponent transferunit is configured and arranged to form at least one additional layer ofthe multilayer device between the first operational layer and the secondoperational layer.
 4. The thermal transfer element of claim 1, furthercomprising a light-to-heat conversion layer disposed between thesubstrate and the multicomponent transfer unit.
 5. The thermal transferelement of claim 1, wherein the multicomponent transfer unit isconfigured and arranged to form, upon transfer to a receptor: an emitterlayer; and an electrode layer.
 6. The thermal transfer element of claim1, wherein the multicomponent transfer unit is configured and arrangedto form, upon transfer to a receptor: a core layer; and a claddinglayer.